He has more then likely damaged the fan trying to remove it.
On these the fan blades can be very tight to remove as it has a opposite thread to remove the bolt and then theres an oilve in the fan blade that is very tight to remove.
Thats the first time ive heard someone drill a hole in the blade. So it will need to be a big hole to get the screw and screwdriver through it so it can effect the balance of the fan and cause the noise.
Even if it isnt the hole thats caused the noise it would be the fan blade thats damaged thats causing this.
They need to replace the fan on this to cure it. What i do to release the fan is spray a bit of WD40 on it and leave it a few minuits and then that helps it to come off.
Now as i said they can be very very tight to come off but they will come off from there.
If you need anymore info just get back to me.